Hi Zen! Sorry for the frustration, we could probably show a "warning" for this in the future. What's happening is, you've pushed two verts (top and bottom) into the exact same position, which creates an impossible surface, and can't be rendered properly. If that doesn't make sense- when you pull those top verts down, and they land exactly on the bottom verts, they bottom ones aren't automatically deleted.
Why aren't they auto-deleted? Well, we've generally tried to not "guess" what the user wants, and do hidden, automatic stuff. So, you'll need to merge those overlaid vertices- try using "Collapse" or "Weld" (make sure "Select Hidden" is on when drag-selecting, to get both vertices).
Hope that helps!

Hi! Great to know the tools are helping Polybrush is still experimental, so use it with caution, ha. However, ProGrids should quickly become your #1 tool to install in every project!
About Polyshape: that "local grid" is only active when editing the Polyshape points. If you start editing it using vertices, edges, etc, it will snap to ProGrids "world" grid- give a test or two and that'll make sense. Just something to be aware of...and something we hope to improve, also, by way of "real" local grids
For placing a prefab onto a surface and using the surface normal for rotation- sorry, that's not something Unity does...yet!

Hi! Sure, you can use Polyshape for this:
When you click to place the first Polyshape point, it adopts the surface normal.
If you are using ProGrids (recommended), that point also becomes the "origin" point of a local grid for the Polyshape object, so you can keep your new shape built on a nice clean grid

Hi! I'm not quite sure what you mean, let me make sure I understand:
"V" is a Unity key that allows you to drag an object from a corner (vert) to another object's corner, on all 3 axis at once (you don't get a choice).
ProBuilder enhances this slightly: when you are in Vertex mode, you can hold "V" and drag on a specific axis, and only that axis will be used- this becomes "aligning" (ie, align to the hovered item on the X axis, etc).
Are you expecting something else, or is this not working for you?
Welcome to the forums!

Hi! If this is a very large object, you probably shouldn't merge it down to a single object. Instead, break it into sections. Otherwise, the game will have to render the entire station, even if the player can only see a small section.

Depending how you count those verts- that's probably a "shared vert" count, but if there's a UV or normal seam, etc, that count could double.
Is there a reason they are using so many polys? The shape is very simple, it would look just fine with a few hundred polys, I think.

EDIT: you beat me to it, yep!
I tried reproducing that look with the existing Smoothing Groups, and couldn't do it- whatever you did there, it looks very nice! You are retaining the flat look on the face, but also smoothing across the bordering edges to it...are you adding geometry/shader? If this is just manipulating normals, I want in!

Ah, thanks for the video! Got it now:
1. Create 2 pb cubes, slightly offset
2. Rotate one cube
3. Set PB handle coords to "Global"
4. Select a vert on the rotated cube
5. Hold V and click-drag on one axis, hover over a vert on other cube - it aligns on that axis only, in Global coords
6. Set PB handle coords to "Local"
7. Hold V and click-drag on one axis, hover over a vert on other cube -
Expected behavior: vert aligns to hovered vert on selected axis only, using Local coords (see Max/Maya for example)
Actual Result: vert snaps on all axis to the hovered vert
Technically, the "V" stuff is Unity- Karl has modified it to work per-axis when editing PB elements. So this might be tricky to fix from PB's end? Good news though: full snapping, alignment, and coordinate space stuff is one of our major goals, now that we're part of Unity